The Role of PPAR Gamma in Fat-Resident Regulatory T Cells and Glucose Homeostasis

描述（由申请人提供）：胰岛素抵抗和2型糖尿病通常伴随肥胖症，并且通过在肥胖状态下发生的脂肪组织的低度慢性炎症与肥胖症相关联.最近，适应性免疫系统的细胞已被证明参与脂肪组织炎症的调节。具体而言，调节性T细胞（Tcells），具有免疫抑制功能的T淋巴细胞的亚群，在瘦而非肥胖小鼠的脂肪组织中富集。这些脂肪驻留TdR（fTdR）可能在抑制炎症和预防内脏脂肪中的胰岛素抵抗中起作用。它们在小鼠内脏脂肪中的丰度与内脏脂肪中的炎症水平以及胰岛素抵抗呈负相关。最近的一项研究表明，与从小鼠脾脏或淋巴结中分离的TcR相比，fTcR具有不同的基因表达特征。特别地，在fT细胞中特异性上调的基因之一是过氧化物酶体增殖物激活受体γ（PPAR 1），脂肪生成和有机体代谢的关键调节剂。此外，初步研究表明，当PPAR！在小鼠中，在TdR中特异性缺失，TdR不再富含内脏脂肪。因此，假设脂肪特异性的fT细胞适应依赖于PPAR的表达和转录活性。在这些细胞中。该建议旨在表征参与上游诱导的PPAR的关键分子机制！及其下游转录靶点。此外，PPAR的必要性！噻唑烷二酮类药物（TZDs）是一类重要的抗糖尿病药物，它是一种PPAR！“激动剂，将使用我们实验室产生的小鼠模型进行研究。首先，它是假设，独特的表达的过氧化物酶体增殖物激活受体！在内脏脂肪组织中，脂肪细胞因子/细胞因子环境是由于内脏脂肪组织内独特的脂肪因子/细胞因子环境。上游信号通路参与的过氧化物酶体增殖体激活受体！将使用体外功能丧失实验来剖析fTdR中的诱导。第二，假设一旦表达，PPAR！以独特的方式作用于重塑fTreg的转录特征，并使fTreg特异性功能，包括维持内脏脂肪中Treg富集和潜在的胰岛素抵抗保护。因此，ChIP-Seq和微阵列表达技术将用于定位PPAR！顺式异构体，并确定关键的过氧化物酶体增殖物激活受体！可能介导fTreg功能的下游靶点。第三，它是假设表达的过氧化物酶体增殖物激活受体！在代谢应激的小鼠中，胰岛素对TZD发挥其全部治疗、胰岛素增敏潜力至关重要。具有Treg特异性PPAR的小鼠！将产生缺失并喂食含或不含TZD的高脂肪饮食。TZD的防护能力 将这些小鼠中胰岛素抗性和代谢综合征的进展与它们的野生型对应物进行比较。总之，这些研究将系统地描述PPAR的作用！并阐明fT 3在肥胖相关的2型糖尿病发病机制中的作用。

DESCRIPTION (provided by applicant): Insulin resistance and type-2 diabetes often accompany obesity and have been linked to obesity by the low- grade chronic inflammation of adipose tissue that occurs in the obese state. Recently, cells of the adaptive immune system have been shown to be involved in the regulation of adipose tissue inflammation. Specifically, regulatory T cells (Tregs), a subset of T lymphocytes with an immunosuppressive function, are enriched in adipose tissue of lean, but not obese, mice. These fat-resident Tregs (fTregs) may have a role in suppressing inflammation and preventing insulin resistance in the visceral fat. Their abundance in the visceral fat of mice inversely correlates with the level of inflammation in the visceral fat as well as insulin resistance. A recent study showed that fTregs have a different gene expression signature compared to Tregs isolated from the spleen or lymph nodes in mice. In particular, one of the genes specifically upregulated in fTregs is peroxisome proliferator-activated receptor gamma (PPAR!), a key regulator of adipogenesis and organismal metabolism. In addition, preliminary studies have shown that when PPAR! is specifically deleted in Tregs in mice, Tregs are no longer enriched in the visceral fat. It is thus hypothesized that th fat-specific adaptation of fTregs is dependent upon the expression and transcriptional activity of PPAR! in these cells. This proposal seeks to characterize the key molecular mechanisms involved in the upstream induction of PPAR!"and its downstream transcriptional targets in fTregs. Furthermore, the necessity of PPAR!"in fTregs for the therapeutic mechanism of action of thiazolidinediones (TZDs), an important anti-diabetic class of drugs that are PPAR!"agonists, will be investigated using a mouse model generated in our lab. First, it is hypothesized that the unique expression of PPAR! in fTregs is due to a distinct adipokine/cytokine milieu within visceral adipose tissue. The upstream signaling pathways involved in PPAR! induction in fTregs will be dissected using in vitro loss-of-function experiments. Second, it is hypothesized that, once expressed, PPAR! acts in a unique way to reshape the transcriptional signature of fTregs and to enable fTreg-specific function, including maintenance of Treg enrichment in visceral fat and potentially protection against insulin resistance. Thus, ChIP-Seq and microarray expression technologies will be used to map the PPAR! cistrome in fTregs and identify key PPAR! downstream targets that could potentially mediate fTreg function. Third, it is hypothesized that expression of PPAR! in fTregs is critical for TZDs to exert their full therapeutic, insulin-sensitizing potential in mice under metabolic stress. Mice with a Treg-specific PPAR! deletion will be generated and fed high fat diet with or without TZD. The ability of TZDs to protect against progression of insulin resistance and metabolic syndrome in these mice will be compared to their wild-type counterparts. Taken together, these studies will systematically characterize the role of PPAR! in fTregs and illuminate the role of fTregs in the pathogenesis of obesity-related type-2 diabetes.